In the International Patent Document WO85/01,911 and the prior United States application mentioned above, a device for mixing thermoplastified synthetic resin has been described in which the device comprises a rotor and a stator defining a gap between them. Both the rotor and the stator, in confronting surfaces bounding the gap, are provided with circumferentially extending rows and axially extending rows of mixing chambers or pockets which are identical and have an elongated outline. The upstream and downstream ends of each of the mixing chamber has a semicircular shape with a given radius. The numbers of mixing chambers in the circumference rows and the axial rows of the rotor coincides with the number of mixing chambers in the corresponding rows of the stator and the circumferential rows of the rotor are offset axially from the circumferential rows of the rotor by about 1/2 the length of the mixing chambers.
The device of the International Application WO85/01911, while generally satisfactory, has been found to be capable of improvement as to mixing efficiency and with respect to the cost of fabrication and the techniques which are required to make such mixing units.
Especially in the case where thermoplastified synthetic resin flows are produced in extruders, it is frequently necessary to incorporate additives such as pigments or other coloring agents in the main flow of the synthetic resin and/or to incorporate therein other synthetic resins and other materials, frequently referred to as "alloying" elements and, in some cases, even a plurality of separate additives. Prior mixing systems have required introducing these materials in the worm-press which has not always proved to be satisfactory.